1. Field of the Invention
The present invention relates to an antenna device for use with a portable wireless apparatus such as, for example, a pager. More particularly, the present invention pertains to a slot antenna device of the type that can be housed in a case and also to a wireless apparatus employing the antenna device.
2. Description of Related Art
Conventionally, portable wireless apparatus such as portable telephones have employed a monopole antenna, an inverted F type antenna and so on, while devices such as pagers have employed a ferrite antenna, a small-loop antenna, a plate type loop antenna and so on. The radiation efficiency or reception efficiency of an antenna, however, is determined by the ratio of the wavelength of electric radiation employed and the size of the antenna. Accordingly, a small antenna, as can be employed in a pager, must be used at a high frequency, and therefore it is impossible to realize a pager that can be used in the FM band and so on. Since a loop antenna, for instance, requires a large aperture in order to be usable in the FM band, it cannot be employed in a pager.